Monitoring and evaluation of fabrication processes on the circuit structures and other types of structures is necessary to ensure the manufacturing accuracy and to ultimately achieve the desired performance of the finished electronic device. With the development trend in miniature devices, the ability to examine microscopic structures and to detect microscopic defects becomes crucial to the fabrication processes.
Various technologies and methods of defect inspection on patterns or structures formed on semiconductor wafers or magnetic arrays have been developed and employed with varying degrees of success. For example, optical inspection methods employ optical inspection tools such, as an optical microscope, the inspect pattern shapes for defects. This type of device usually involves collecting radiation emitted from a target or scattered by a target from an incident beam of radiation directed at the structure. The collected radiation is converted to signals that can be measured or used to form an image. Such measurements or images can be used to determine various characteristics, such as the profile of the structure. Additionally, for wafer topography, electric sensors, such as capacitive sensors, have been employed to measure variations in substrate height. Such sensors detect changes in capacitance due to variations in topography as a sensor element is scanned across a target. The height of the sensor is typically controlled by a height transducer such as a piezoelectric element, which keeps the sensor element at a fixed height above the target structure. Changes in the signals that drive the height transducer can be analyzed to determine the profile of the structure.
With respect to magnetic samples, magnetic microscopy has been widely used in many areas of research for imaging and characterizing the samples. Suitable applications for the magnetic microscope include failure analysis, fault isolation, inspection of semiconductor integrated circuit, manufacturing monitoring and other biological, chemistry, physics and materials research applications. Specifically, many physical objects (e.g., conductors or semiconductors) generate magnetic fields near the objects surfaces when a current flows inside them. The magnetic microscope can obtain images of the magnetic fields by scanning a magnetic sensor on the surface of the object of interest. With the images of the magnetic fields, it is possible to reconstruct the path followed by the currents and consequently localize any defects. Additionally, the magnetic field is not perturbed by non-ferromagnetic materials, and thus, a map of the currents may be produced without de-processing the device. Accordingly, it avoids the risk of losing the defect by de-packaging the component in the localization stage. There are currently a number of techniques for imaging magnetic fields at surfaces. The conventional scanning magnetic microscope has a microscopic field sensor, typically a superconducting quantum interference device (SQUID), a Hall probe or simply a magnetic tip. This type of microscope scans the magnetic sensor relative to a sample to obtain a local field image. The magnetic sensor is typically controlled by a magnetic transducer such as a piezoelectric element.
It is within this context that aspects of the present disclosure arise.